With Automatic Transmission

ALLISON AUTOMATIC TRANSMISSION

DTC P0500 (8.1L)





Circuit Description for Allison Automatic Transmission
The vehicle speed sensor (VSS) monitors the rotation speed of the transmission output shaft. The VSS assembly is a permanent magnet generator. It produces an AC voltage as the rotor teeth on the output shaft of the transmission, 2WD, or transfer case, 4WD, pass through the magnetic field of the sensor. The AC voltage frequency and amplitude increase as the vehicle speed increases. The transmission control module (TCM) will send a controlled duty cycle voltage to the powertrain control module (PCM) that operates in a range of -4.5 volts or +5.0 volts. The PCM converts this signal into vehicle speed. As vehicle speed increases, the frequency of the duty cycle will increase.
DTC P0500 is a type B DTC.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0500 Vehicle Speed Sensor (VSS) Circuit

Conditions for Running the DTC
^ The engine is running.
^ The engine coolant temperature (ECT) is greater than 25°C (77°F).

Conditions for Setting the DTC
^ If the PCM detects a difference in vehicle speed with the VSS of greater than 8 km/h (5 mph), then DTC P0500 is set.
^ No vehicle speed with engine RPM greater than 1,000 RPM and engine torque more than 300 Nm (221 ft. lbs.).

Action Taken When the DTC Sets
^ The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs.
^ The PCM disables cruise control.
^ The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
^ The PCM stores DTC P0500 in PCM history.

Conditions for Clearing the MIL/DTC
^ The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
^ A scan tool can clear the MIL/DTC.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Test Description








The numbers below refer to the step numbers on the diagnostic table.
4. This step tests the TCM and circuit 400 for voltage at the PCM connector.
5. This step tests for continuity and a short to ground in the wiring system between the TCM and PCM.